/**
 * Copyright 2005 The Apache Software Foundation
 * <p>
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * <p>
 * http://www.apache.org/licenses/LICENSE-2.0
 * <p>
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.hadoop.mapred;

import java.io.IOException;
import java.io.File;
import java.io.DataInput;
import java.io.DataOutput;

import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.UTF8;
import org.apache.hadoop.fs.FileSystem;

/**
 * A section of an input file.  Returned by {@link
 * InputFormat#getSplits(FileSystem, JobConf, int)} and passed to
 * InputFormat#getRecordReader(FileSystem,FileSplit,JobConf,Reporter).
 */
public class FileSplit implements Writable {
    private File file;
    private long start;
    private long length;

    FileSplit() {
    }

    /**
     * Constructs a split.
     *
     * @param file   the file name
     * @param start  the position of the first byte in the file to process
     * @param length the number of bytes in the file to process
     */
    public FileSplit(File file, long start, long length) {
        this.file = file;
        this.start = start;
        this.length = length;
    }

    /**
     * The file containing this split's data.
     */
    public File getFile() {
        return file;
    }

    /**
     * The position of the first byte in the file to process.
     */
    public long getStart() {
        return start;
    }

    /**
     * The number of bytes in the file to process.
     */
    public long getLength() {
        return length;
    }

    @Override
    public String toString() {
        return file + ":" + start + "+" + length;
    }

    ////////////////////////////////////////////
    // Writable methods
    ////////////////////////////////////////////

    /**
     * @author shen
     * @date 2021/10/14
     * 描述：
     * 1、写如文件名
     * 2、写入文件的字节的开始位置
     * 3、写入文件的长度
     */
    @Override
    public void write(DataOutput out) throws IOException {
        UTF8.writeString(out, file.toString());
        out.writeLong(start);
        out.writeLong(length);
    }

    /**
     * @author shen
     * @date 2021/10/14
     * 描述：
     * 1、和{@link FileSplit#write}作用相反
     * 
     */
    @Override
    public void readFields(DataInput in) throws IOException {
        file = new File(UTF8.readString(in));
        start = in.readLong();
        length = in.readLong();
    }


}
